• Ming Lei's avatar
    genirq, sched/isolation: Isolate from handling managed interrupts · 11ea68f5
    Ming Lei authored
    The affinity of managed interrupts is completely handled in the kernel and
    cannot be changed via the /proc/irq/* interfaces from user space. As the
    kernel tries to spread out interrupts evenly accross CPUs on x86 to prevent
    vector exhaustion, it can happen that a managed interrupt whose affinity
    mask contains both isolated and housekeeping CPUs is routed to an isolated
    CPU. As a consequence IO submitted on a housekeeping CPU causes interrupts
    on the isolated CPU.
    
    Add a new sub-parameter 'managed_irq' for 'isolcpus' and the corresponding
    logic in the interrupt affinity selection code.
    
    The subparameter indicates to the interrupt affinity selection logic that
    it should try to avoid the above scenario.
    
    This isolation is best effort and only effective if the automatically
    assigned interrupt mask of a device queue contains isolated and
    housekeeping CPUs. If housekeeping CPUs are online then such interrupts are
    directed to the housekeeping CPU so that IO submitted on the housekeeping
    CPU cannot disturb the isolated CPU.
    
    If a queue's affinity mask contains only isolated CPUs then this parameter
    has no effect on the interrupt routing decision, though interrupts are only
    happening when tasks running on those isolated CPUs submit IO. IO submitted
    on housekeeping CPUs has no influence on those queues.
    
    If the affinity mask contains both housekeeping and isolated CPUs, but none
    of the contained housekeeping CPUs is online, then the interrupt is also
    routed to an isolated CPU. Interrupts are only delivered when one of the
    isolated CPUs in the affinity mask submits IO. If one of the contained
    housekeeping CPUs comes online, the CPU hotplug logic migrates the
    interrupt automatically back to the upcoming housekeeping CPU. Depending on
    the type of interrupt controller, this can require that at least one
    interrupt is delivered to the isolated CPU in order to complete the
    migration.
    
    [ tglx: Removed unused parameter, added and edited comments/documentation
      	and rephrased the changelog so it contains more details. ]
    Signed-off-by: default avatarMing Lei <ming.lei@redhat.com>
    Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
    Link: https://lore.kernel.org/r/20200120091625.17912-1-ming.lei@redhat.com
    11ea68f5
kernel-parameters.txt 194 KB